1. Field of the Invention
This invention relates to aqueous compositions containing an alkylbenzene contrast agent and methods for its use in diagnostic radiology of the gastrointestinal tract.
2. Reported Developments
Roentgenographic examination utilizing X-rays and computed tomography (hereinafter CT) scans of fractures and other conditions associated with the skeletal system is routinely practiced without the use of contrast agents. X-ray visualization of organs containing soft tissue, such as the gastrointestinal (hereinafter GI) tract, requires the use of contrast agents which attenuate X-ray radiation. D.P. Swanson et al in "Pharmaceuticals In Medical Imaging", 1990, MacMillan Publishing Company, provides an excellent background in medical imaging utilizing contrast agents and compositions therewith.
Roentgenographic examination of the GI tract are indicated for conditions of digestive disorders, changes in bowel habit, abdominal pain, GI bleeding and the like. Prior to radiological examination, administration of a radiopaque contrast medium is necessary to permit adequate delineation of the respective lumen or mucosal surface from surrounding soft tissues. Accordingly, a contrast medium is administered orally to visualize the mouth, pharynx, esophagus, stomach, duodenum and proximal small intestine. The contrast medium is administered rectally for examination of the distal small intestine and the colon.
The most widely used contrast agent for the visualization of the GI tract is barium sulfate administered as a suspension orally or rectally as an enema. (See, for example, U.S. Pat. Nos.: 2,659,690; 2,680,089; 3,216,900; 3,235,462; 4,038,379 and 4,120,946) Notwithstanding its relatively good contrast characteristics, negligible absorption from the GI tract following oral or rectal administration and speedy excretion from the body, barium sulfate has certain disadvantages. In the presence of intestinal fluids it lacks homogeneity and poorly adheres to mucus membranes which can result in poor X-ray images. In the colon, when administered as an enema, it flocculates and forms irregular clumps with fecal matter.
Iodinated organic compounds have also been used as GI contrast agents since the iodine atom is an effective X-ray absorber. They have the most versatility and are utilized in the widest variety of procedures. They are very absorptive of X-rays with which the iodine interacts and produce a so-called photoelectric effect which is a large magnification in contrast caused by the photons stopped in the iodine-containing medium. The magnification of contrast exceeds the level that would be expected from relative changes in density. Because of this magnification, relatively low concentrations of the contrast agent can be utilized. (For iodinated agents see, for example, U.S. Pat. Nos.: 2,786,055; 3,795,698; 2,820,814; 3,360,436; 3,574,718, 3,733,397; 4,735,795 and 5,047,228.)
The desiderata for an ideal GI contrast agent includes: good toxicological profile; the ability to fill the entire bowel/lumen and evenly coat the gut mucosa so that the presence of the bowel is detectable when the lumen is not distended; and nonirritation to the intestinal mucosa; and passage through the GI tract without producing artifacts or stimulating vigorous intestinal peristalsis.
We have found that compounds having these and other desirable characteristics in the GI tract should preferably have the following properties for inclusion in a suitable pharmaceutically acceptable vehicle for oral or rectal administration:
a partition coefficient, i.e. the ratio of hydrophobicity to hydrophilicity of about 10 or higher; PA0 a melting point of less than about 80.degree. C.; and PA0 a molecular weight of at least about 200. PA0 a partition coefficient of about 10 or higher, and preferably, from about 10.sup.2 to about 10.sup.8 ; PA0 a melting point of less than 80.degree. C., and preferably less than 60.degree. C.; and PA0 a molecular weight of at least 200, and preferably from about 200 to about 2,000; and PA0 a pharmaceutically acceptable aqueous carrier therefor. PA0 a partition coefficient of about 10 or higher, and preferably, from about 10.sup.2 to about 10.sup.8 ; PA0 a molecular weight of at least 200, and preferably from about 200 to about 2,000; and PA0 a pharmaceutically acceptable aqueous carrier therefor.
We have found that certain compounds hereinafter described possess these desirable properties when used in aqueous oral and rectal formulations for examination of the GI tract utilizing X-rays and CT scans.